Gain scheduling control of variable speed WTG under widely varying turbulence loading

Probabilistic paradigms for wind turbine controller design have been gaining attention. Motivation derives from the need to replace outdated empirical-based designs with more physically relevant models. This paper proposes an adaptive controller in the form of a linear quadratic Gaussian (LQG) for control of a stall-regulated, variable speed wind turbine generator (WTG). In the control scheme, the strategy is twofold: maximization of energy captured from the wind and minimization of the damage caused by mechanical fatigue due to variation of torque peaks generated by wind gusts. Estimated aerodynamic torque and rotational speed are used to determine the most favorable control strategy to stabilize the plant at all operating points (OPs). The performance of the proposed controller is compared with the classical proportional-integral-derivative (PID) controller. The LQG is seen to be significantly more efficient especially in the alleviation of high aerodynamic torque variations and hence mechanical stresses on the plant drive train. Simulation results validate the effectiveness of the proposed method.     

On-line designed hybrid controller with adaptive observer for variable-speed wind generation system

This paper presents a wind-driven induction generator system with a hybrid controller, which combines the advantages of the integral–proportional and the sliding mode controllers. The proposed controller is designed to adjust the turbine speed to extract maximum power from the wind. The integral–proportional speed controller can be designed on-line according to the estimated rotor parameters, and the observed disturbance torque is feed-forward to increase the robustness of the system. The designed integral switching surface with integral–proportional due to on-line tuning produced a new sliding surface to implement the control, and can ensure the robustness under noisy environment. The rotor inertia constant, friction constant, and the disturbed mechanical torque of the induction generator are estimated by a proposed adaptive observer, which is composed of the recursive least square algorithm and a torque observer.     

Design of a wind turbine pitch angle controller for power system stabilisation

The design of a PID pitch angle controller for a fixed speed active-stall wind turbine, using the root locus method is described in this paper. The purpose of this controller is to enable an active-stall wind turbine to perform power system stabilisation. For the purpose of controller design, the transfer function of the wind turbine is derived from the wind turbine's step response. The performance of this controller is tested by simulation, where the wind turbine model with its pitch angle controller is connected to a power system model. The power system model employed here is a realistic model of the North European power system. A short circuit fault on a busbar close to the wind turbine generator is simulated, and the dynamic responses of the system with and without the power system stabilisation of the wind turbines are presented. Simulations show that in most operating points the pitch controller can effectively contribute to power system stabilisation.     

Aggregated dynamic model for wind farms with doubly fed induction generator wind turbines

As a result of increasing wind farms penetration in power systems, the wind farms begin to influence power system, and thus the modelling of wind farms has become an interesting research topic. Nowadays, doubly fed induction generator based on wind turbine is the most widely used technology for wind farms due to its main advantages such as high-energy efficiency and controllability, and improved power quality. When the impact of a wind farm on power systems is studied, the behavior of the wind farm at the point common coupling to grid can be represented by an equivalent model derived from the aggregation of wind turbines into an equivalent wind turbine, instead of the complete model including the modelling of all the wind turbines. In this paper, a new equivalent model of wind farms with doubly fed induction generator wind turbines is proposed to represent the collective response of the wind farm by one single equivalent wind turbine, even although the aggregated wind turbines operate receiving different incoming winds. The effectiveness of the equivalent model to represent the collective response of the wind farm is demonstrated by comparing the simulation results of equivalent and complete models both during normal operation and grid disturbances.     

Simulation model for wind turbine with asynchronous generator interconnected to the electric network

This paper presents the study of a structure composed of a wind turbine, a speed multiplier and an asynchronous generator coupled to the infinite power network through a line of energy transfer electric modelled by an R–L circuit. After modelling of the global system, the behaviour of the proposed structure in steady states and in transient regimes is studied. The problem of the electric energy transfer to the network was studied. On the other hand, if the wind speed changes too much variation, this will cause a violent variation of power and result in step out operation of the generator from the power system. This paper proposes a control strategy to reduce the power variations by introducing feed forward control combined with conventional feedback control.     

Study on power performance for straight-bladed vertical axis wind turbine by field and wind tunnel test

In this paper, the power performance of straight-bladed VAWT is experimentally investigated by wind tunnel experiment and field test. The test rotor is two-bladed with NACA0021 airfoil profile. A survey of varying unsteady wind parameters is conducted to examine the effects of blade pitch angle, Reynolds number and wind velocity on the power performance of VAWT. Moreover, the flow field characteristics are obtained through measuring the wind velocity by Laser Doppler Velocimeter (LDV) system in the wind tunnel experiment and three-cup type anemometers in field test. Power and torque performance are obtained through a torque meter installed in rotor shaft of the wind turbine. Experimental results estimated from the measured values from field test and wind tunnel experiment are compared. In this research, power performance and flow field characteristics are discussed and the relationship between operating conditions and wind velocity are verified. These results provided a theoretical guiding significance to the development of VAWT simplified.     

Analytical model for predicting the performance of photovoltaic array coupled with a wind turbine in a stand-alone renewable energy system based on hydrogen

We present the results of an analysis of the performance of a photovoltaic array that complement the power output of a wind turbine generator in a stand-alone renewable energy system based on hydrogen production for long-term energy storage. The procedure for estimating hourly solar radiation, for a clear sunny day, from the daily average solar insolation is also given. The photovoltaic array power output and its effective contribution to the load as well as to the energy storage have been determined by using the solar radiation usability concept. The excess and deficit of electrical energy produced from the renewable energy sources, with respect to the load, govern the effective energy management of the system and dictate the operation of an electrolyser and a fuel cell generator. This performance analysis is necessary to determine the effective contribution from the photovoltaic array and the wind turbine generator and their contribution to the load as well as for energy storage.     

A novel online training neural network-based algorithm for wind speed estimation and adaptive control of PMSG wind turbine system for maximum power extraction

In this paper, an adaptive control scheme for maximum power point tracking of stand-alone PMSG wind turbine systems (WTS) is presented. A novel procedure to estimate the wind speed is derived. To achieve this, a neural network identifier (NNI) is designed in order to approximate the mechanical torque of the WTS. With this information, the wind speed is calculated based on the optimal mechanical torque point. The NNI approximates in real-time the mechanical torque signal and it does not need off-line training to get its optimal parameter values. In this way, it can really approximates any mechanical torque value with good accuracy. In order to regulate the rotor speed to the optimal speed value, a block-backstepping controller is derived. Uniform asymptotic stability of the tracking error origin is proved using Lyapunov arguments. Numerical simulations and comparisons with a standard passivity based controller are made in order to show the good performance of the proposed adaptive scheme.     

Experimental performance assessment of an online energy management strategy for varying renewable power production suppression

Lately, interest in renewable sources, especially wind and solar energy, has shown a significant increase in all over the world that mostly depends on climate-threatening conventional fossil fuels. Besides, hybrid use of these power sources with suitable back-up units provides many advantages compared to sole use of these sources. In this regard, a hybrid system consisting of a wind turbine for utilizing the wind energy, photovoltaic panels for solar energy, fuel cell for providing back-up power and a battery unit for storing the possible excess energy production and supplying the transient load is considered in this study. Experimental assessment of this system in different case studies including the real time measured dynamic power demand of an office block is realized. The collaborative actions of the proposed hybrid system with a fuzzy logic based energy management strategy during fluctuations of renewable-based power production are investigated. Thus, results of this study may be valuable for evaluating the feasibility of stand-alone hybrid renewable energy units for future power systems.     

Autonomous BDFIG-wind generator with torque and pitch control for maximum efficiency in a water pumping system

This paper presents and analyzes the operation strategy for an autonomous wind energy conversion system oriented to water pumping. It consists of a wind turbine with a Brushless Doubly-Fed Induction Generator (BDFIG), electrically coupled with a squirrel cage induction machine moving a centrifugal type water pump. Because of no brushes and slip rings, the BDFIG is suitable for autonomous systems, which often work in hard conditions. Additionally, the power flow on the BDFIG principal stator could be driven from a fractional power converter connected on the auxiliary stator winding. This Turbine-BDFIG and Motor-Pump configuration provides a high robustness and reliability, reducing the operational and maintenance costs. The operation strategy proposes, for wind speeds smaller than the rated, to maximize the volume of water pumped based on the optimization of the wind energy capture. To do that, a sliding mode control tracks the optimal turbine torque by means of a torque control. Meanwhile, for wind speeds greater than the rated, a pitch control keeps the water pump within the safe operation area by adjusting the speed and power of the turbine in their rated values. To assess and corroborate the proposed strategy, simulations with different wind profiles are made.     

General study of the control principles and dynamic fault behaviour of variable-speed wind turbine and wind farm generic models

The interest towards generic models or sometimes also called standard models of wind turbine generators (WTGs) is significantly increasing. Mainly due to their improved power quality, better controllability and higher power extraction capability, variable-speed wind turbines driving a synchronous or an induction machine are capturing the global market. Throughout this paper, dynamic modelling and performance analysis of the generic models of the variable-speed WTGs, namely the doubly-fed induction generator and the fully-rated converter based WTGs, are achieved using integration between Matlab/Simulink and PSCAD/EMTDC simulation platforms. Later on, the performance of type-4 wind turbine driving a permanent magnet synchronous machine is analysed during fault and then compared with the case when driving a wound rotor induction machine. The differences in control principles and dynamic fault behaviour are highlighted. Afterwards, investigations on wind farm level are accomplished. A case study during which the developed generic models and the generic model of the variable-speed machine are compared is conducted. Different arrangements for the construction of the generic wind farm are considered.     

Validation of fixed speed wind turbine dynamic models with measured data

Power system dynamics studies involving fixed-speed wind turbines normally use a wind turbine model consisting of two lumped masses, an elastic coupling and a induction generator model which neglects stator transients. However, validations of this model with measured data are rarely reported in the literature. This paper validates the model using a recorded case obtained in a fixed speed, stall regulated 180 kW wind turbine through a voltage dip. The work analyses the performance of the reduced order induction generator model which neglects stator transients, compared to the detailed induction generator model. It also includes a study of the convenience of representing mechanical damping in the drive train, and an evaluation of the single mass mechanical model.     

Design and coordination of a capacitor and on‐load tap changer system for voltage control in a wind power plant of doubly fed induction generator wind turbines

Larger percentages of wind power penetration into the grid translate to more demanding requirements coming from grid codes; for example, voltage support at the point of connection has been introduced recently by several grid codes from around the world, thus making it important to analyse this control. Voltage control is actuated by reactive power injection, and for a wind power plant of doubly fed generator turbines, reactive power capability can be a challenge, which typically is overcome by installing reactive power compensators. The integration and the interaction between all these reactive power sources and the on‐load tap changer of the main substation transformer need to be analysed and taken into account in the control design. In this paper, a novel coordination and control strategy for capacitor banks and on‐load tap changer for a wind power plant is introduced. The capacitor banks are controlled in such way that the steady‐state usage of the converters for reactive power injection is driven below to a maximum desired value of 0.1 pu. Additionally, the control transients because of the capacitor bank switching are minimized by using a suitable control structure. The tap changer control is coordinated with the plant control to decrease the impact of the capacitors reactive power in the line drop calculation, thus reducing the amount of tap operations and improving the accuracy of the line drop voltage estimation. The coordination of the central controller with the plant components is analysed and tested through electromagnetic transient program simulations. Copyright © 2011 John Wiley & Sons, Ltd.     

Terminal voltage build-up and control of a DFIG based stand-alone wind energy conversion system

The paper presents the voltage build-up process and the terminal voltage control of a doubly-fed induction generator (DFIG) driven by a pitch controlled wind turbine for the supply of autonomous system without any auxiliary source. A control strategy for the complete system including voltage build-up phase is developed with a view to provide as well as possible the required power for load. Indirect stator flux-oriented vector control is proposed to keep the stator voltage constant by means of a back-to-back converter connected to the rotor side, while the management system is supported by the pitch angle and the load shedding controllers. A novel scheme for voltage build-up is presented, which requires no additional hardware support, and physical interpretation of how self-excitation can occur from residual magnetism in the machine core is examined. A reliable start-up process is accomplished by using an appropriate voltage reference ramp which enables minimizing energy loss during the starting. The proposed system is modeled and simulated using Matlab/Simulink software program to examine the dynamic characteristics of the system with proposed control strategy. Dynamic simulation results for different transient conditions demonstrate the effectiveness of the proposed control strategy.     

New strategy of pitch angle control for energy management of a wind farm

In this paper, we are interested in a Wind Energy Conversion System (WECS) based on a Permanent Magnetic Synchronous Generator (PMSG). The studied WECS is made by the association of three aerogenerators. The objective of this work is to investigate a new strategy of pitch angle control to ensure a balance between the produced energy and the demanded one by the loads. The control strategy of the wind farm is composed of two parts: a local control according to the characteristics of each wind turbine « Pitch control » to protect the turbines against mechanical failure in the event of wind gust and a global control according to the total power demand and the available wind power. This strategy leads to achieving power objectives (active and reactive power targets) and system constraints.     

Performance of a 3 kW wind turbine generator with variable pitch control system

A prototype 3 kW horizontal upwind type wind turbine generator of 4 m in diameter has been designed and examined under real wind conditions. The machine was designed based on the concept that even small wind turbines should have a variable pitch control system just as large wind turbines, especially in Japan where typhoons occur at least once a year. A characteristic of the machine is the use of a worm and gear system with a stepping motor installed in the center of the hub, and the rotational main shaft. The machine is constructed with no mechanical breaking system so as to avoid damage from strong winds. In a storm, the wind turbine is slowed down by adjusting the pitch angle and the maximum electrical load. Usually the machine is controlled at several stages depending on the rotational speed of the blades. Two control methods have been applied: the variable pitch angle, and regulation of the generator field current. The characteristics of the generator under each rotational speed and field current are first investigated in the laboratory. This paper describes the performances of the wind turbine in terms of the functions of wind turbine rotational speed, generated outputs, and its stability for wind speed changes. The expected performances of the machine have been confirmed under real wind conditions and compared with numerical simulation results. The wind turbine showed a power coefficient of 0.257 under the average wind speed of 7.3 m/s.     

Comparative study on the performance of control systems for doubly fed induction generator (DFIG) wind turbines operating with power regulation

As a result of the increasing wind power penetration on power systems, the wind farms are today required to participate actively in grid operation by an appropriate generation control. This paper presents a comparative study on the performance of three control strategies for DFIG wind turbines. The study focuses on the regulation of the active and reactive power to a set point ordered by the wind farm control system. Two of them (control systems 1 and 2) are based on existing strategies, whereas the third control system (control system 3) presents a novel control strategy, which is actually a variation of the control system 2. The control strategies are evaluated through simulations of DFIG wind turbines, under normal operating conditions, integrated in a wind farm with centralized control system controlling the wind farm generation at the connection point and computing the power reference for each wind turbine according to a proportional distribution of the available power. The three control systems present similar performance when they operate with power optimization and power limitation strategies. However, the control system 3 with down power regulation presents a better response with respect to the reactive power production, achieving a higher available reactive power as compared with the other two. This is a very important aspect to maintain an appropriate voltage control at the wind farm bus.     

离网型户用风力发电机性能测试系统的开发

本文为离网型户用风力发电机虚拟仪器性能测试系统的研制 ,利用NI公司推出的软件LabVIEW及相关配套硬件设备 ,设计了风力机基本性能参数的测试系统。通过对风力发电机输出电流、输出电压、大气温度、大气压力、风速等实验数据的分析和处理 ,得到风力发电机输出特性曲线 ,从而为评估和改进风力发电机的性能提供依据     

Study of a double fed induction generator using matrix converter: Case of wind energy conversion system

Due to the growing of the power electronics, especial attention has been given to the use of new generation of power converters, AC/AC matrix converter to which provide a direct power converter AC/AC, bi-directional power flow, almost sinusoidal input and output waveform. In this paper, we present the performance study of a variable-speed wind turbine based on doubly fed induction generator fed by matrix converter using the maximum power point tracking method to extract the maximum power available. The whole system is presented in d-q-synchronous reference frame. The control scheme is tested and the performances are evaluated by simulation results. The simulation results obtained under MatLab/Simulink show the effectiveness and validity of the considered control.